In separate pans cook the potatoes and carrots in salted water for 15 minutes, drain and cool.
Drop beans into a pan of boiling salted water, cover and cook for 6-8 minutes, drain and cool.
Cut the cucumbers into quarters and place in a shallow dish with potatoes, carrots and beans.
Spread the dressing over, baste well, cover and chill for 2-3 hours.